AIMS: Internationally, the implementation of diagnosis-related group systems has underlined the importance of quality assurance and improvement in health care systems. Support is expected by various concepts based on different theories and traditions. Published experience and knowledge of other countries with long-standing DRG systems and data in literature are studied to see whether there is an evidence-based impact of quality assurance and quality improvement on health care systems. METHODS: Relevant data was searched for in the Cochrane-database, the INAHTA-databases DARE, NHSEED and HTA, in DIMDI and the Medline-database of the NIH as well as generally in the internet, addressing the different countries. RESULTS: Several tools of quality assurance and quality improvement like accreditation, evidence-based medicine and guidelines exist in most of the 18 countries studied. Some of them, such as registries and audits, have marked national characteristics. Similar problems in provision of health care are reported internationally. There is broad consensus as to the aspects to be addressed in quality improvement concepts. Though international consensus on effective organization and methods of external assessment is growing there is only limited evidence for efficiency and general applicability of the different tools. Their cost impact, too, has not undergone systematic evaluation. Procedures like feedback strategies and reflection have been identified as having the potenzial to change the practice of health care professionals on a local level, but evidence for system-related impact is missing. Above all, for all concepts of quality improvement there is no real evidence of clinical benefit in the sense of better patient outcomes. CONCLUSIONS: None of the various tools for quality improvement in health care proves superior so far. It remains unclear which tool suits best for which intended improvement and in which context. Although quality improvement as a strategy meets with wide approval and appears to be a correct health policy, it remains doubtful whether it really improves clinical outcome and patient-centred health care. Public health research should address these questions. New concepts (e. g. integrating different tools of quality assurance and improvement or DMP systems) need evaluation prior to their broad implementation. Social medicine is called upon to mediate between the consented health care aims of society and medicine.